Yes, that looks like a malware site with a fake Firefox malware window showing, so do not click that button.
That site may have been hacked if you get redirected.
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Just to be sure, you can do a malware check with some malware scanning programs on the Windows computer.<br />
You need to scan with all programs because each program detects different malware.
Make sure that you update each program to get the latest version of their databases before doing a scan.
*Malwarebytes' Anti-Malware:<br>http://www.malwarebytes.org/mbam.php
*SuperAntispyware:<br>http://www.superantispyware.com/
*Microsoft Safety Scanner:<br>http://www.microsoft.com/security/scanner/en-us/default.aspx
*Windows Defender: Home Page:<br>http://www.microsoft.com/windows/products/winfamily/defender/default.mspx
*Spybot Search & Destroy:<br>http://www.safer-networking.org/en/index.html
*Kasperky Free Security Scan:<br>http://www.kaspersky.com/security-scan
You can also do a check for a rootkit infection with TDSSKiller.
*http://support.kaspersky.com/viruses/solutions?qid=208280684
See also:
*"Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked